Until recently, windows were built in buildings with a vertical void placed on either side of the window itself. In this void, a weight was attached to the window via a pulley and rope and used to counterbalance the weight of the window. The window could be partially or completely opened, and the weights would prevent the spontaneous closure of the window by gravity. The weights were designed to travel freely up and down the void as the window is closed and opened.
Today, newly manufactured windows use friction or some other method to remain open and no longer need counterbalance weights. However, when existing windows of the older design are replaced with the newer windows, the adjacent voids remain in the wall.
When unfilled, these voids can be a source of significant heat loss through the wall. As most windows are replaced for the purpose of energy conservation, the filling of these voids can be critical to the success of a window replacement project. The remaining voids must be filled with insulation in order to prevent significant heat loss through the wall.
Presently, these voids can be filled by injecting polyurethane foam into the void (see U.S. Pat. No. 5,273,693 to Rothwell et al.). However, foam injection entails significant cost due to the both the expense of the material and the handling difficulties associated with this potentially toxic substance.
What is needed is a simple, effective method of filling voids in structures with insulating material.